10Base-T and 100Base-TX (hereafter referred to as 10/100Base-T Ethernet) are Ethernet protocols defined in the IEEE 802.3 Ethernet specification for transmission of Ethernet signals over a network cable at 10 Mbps and 100 Mbps respectively. The network cable (e.g., Cat5E cable) usually consists of four twisted pairs, of which one twisted pair carries Ethernet signal sent from one network device to a connected network device and another twisted pair carries Ethernet signal sent in the opposite direction between the two connected network devices. The remaining two twisted pairs are left unused. The two twisted pairs that carry bi-directional Ethernet signals are usually referred to as data pairs and the two unused twisted pairs are usually referred to as spare pairs.
With the advent of Power-over Ethernet (PoE) technology, electrical power from a network device can also be delivered to a connected network device over a shared network cable so that the connected network device can be advantageously powered without a separate power cord. According to the PoE technology as defined in the IEEE 802.3af and 802.3at specification, the network device which outputs electrical power onto the shared network cable is referred to as a Power Source Equipment (PSE) such as an Ethernet switch with the PoE capability, and the connected network device which receives electrical power from the PSE over the shared network cable is referred to as a Power Device (PD) such as a PoE powered IP (Internet Protocol) phone. Specifically, there are two power delivery modes referred to as “Mode A” and “Mode B” for delivering electrical power over the shared network cable according to the PoE specification. “Mode A” uses the two data pairs of a network cable for delivering electrical power, and “Mode B” uses the two spare pairs of a network cable for delivering electrical power; a PSE usually supports either “Mode A” or “Mode B”, and a PD must support both “Mode A” and “Mode B”. “Mode A” and “Mode B” are also commonly referred to as Endspan and Middlespan, respectively. It can be seen that for a 10/100Base-T PSE operating in “Mode A”, only the two data pairs of a network cable are used.
Although 10/100Base-T Ethernet technology and the PoE technology were originally developed for transmission of Ethernet signals and electrical power over a network cable of four twisted pairs or at least two twisted pairs, there have been great commercial interests in techniques for transmission of 10/100Base-T Ethernet signals (4-wire based signals) and electrical power over a coaxial cable which is a 2-wire transmission medium. For example, as more and more video surveillance systems worldwide are migrating from analog video systems to IP camera based digital video systems, techniques of transmission of 10/100Base-T Ethernet signals and electrical power over a coaxial cable can make it possible to reuse the existing coaxial cables in a retired analog video system for transmission of IP videos and for delivering electrical power to power IP cameras, which can bring down overall system costs significantly by not having to install new network cables.
In view of the foregoing, there is a need for improved and more cost-effective system, apparatus and method for transmission of Ethernet signals and electrical power over a coaxial cable.